This invention pertains to water jet propulsion systems and more particularly to such a system provided with a variable thrust controller.
Propulsion systems for boats employing a jet of water discharged from the stern of the boat have become increasingly popular. Propulsion systems of the kind described have been arranged to provide a forward thrust to the boat and, by lowering a gate across the end of the discharging nozzle the discharge of water is diverted downwardly and forwardly through a secondary flow passage so as to cause the boat to slow or reverse its direction of travel by applying a reversing thrust.
In a propulsion system of the kind described an impeller provides a flow of water through a discharging nozzle so as to drive the boat forwardly as noted. The impeller in turn is driven by an engine and, in order to adjust the speed of the boat the impeller is driven faster or slower by an engine coupled thereto. Accordingly, at a certain point in time the impeller and motor are operating at full speed and additional speed is not then available. However, there has been a need for the provision of an improved propulsion system in which additional speed can be obtained over and above that obtained from maximum operation of the engine and impeller system.
As disclosed herein means are provided for constricting the opening of the nozzle so as to increase the velocity of the water being discharged from the nozzle and in this way increase the thrust and speed of the boat.
In addition, when racing with boats of the kind described the boats sometimes have had a tendency to bob up and down in a cyclic manner much akin to the movements of a porpoise and therefore referred to as "porpoising" by most boat operators.
As disclosed herein means are provided for overcoming this "porpoising" movement by selectively directing the jet discharge stream upwardly or downwardly to the rear as desired.
In addition to the above, propulsion systems of the kind noted presently can be provided with a downwardly and forwardly open secondary flow passage for applying a reverse thrust to the boat in response to closing of the rearwardly directed nozzle by means of a gate. Thus, as the gate is closed the only escape for water from the impeller is downwardly and forwardly through the secondary flow passage which thereby applies the rearward thrust to the boat. It has been observed that the presence of the continuously open secondary flow passage can serve to reduce the thrust of the rearwardly moving jet stream of water. Accordingly, there has been a need for an improved water jet propulsion system of the kind described having means for adjusting the thrust derived from the stream.